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A finite strain nonlinear constitutive model is presented to study the extreme mechanical behavior of a polyurethane-urea well suited for many engineering applications. The micromechanically- and thermodynamically based constitutive model captures salient features in resilience and dissipation in the material at low to high strain rate. The extreme deformation features are further elucidated by laser-induced micro-particle impact tests for the material, where an ultrafast strain rate ($>10^6$ s$^{-1}$) incurs. Numerical simulations for the strongly inhomogeneous deformation events are in good agreement with the experimental data, supporting the predictive capabilities of the constitutive model for the extreme deformation features of the PUU material over at least 9 orders of magnitude in strain rates ($10^{-3}$ to $10^{6}$ s$^{-1}$).

High-velocity microparticle impacts are relevant to many fields from space exploration to additive manufacturing and can be used to help understand the physical and chemical behaviors of materials under extreme dynamic conditions. Recent advances in experimental techniques for single microparticle impacts have allowed fundamental investigations of dynamical responses of wide-ranging samples including soft materials, nano-composites, and metals, under strain rates up to 108 s-1. Here we review experimental methods for high-velocity impacts spanning 15 orders of magnitude in projectile mass and compare method performances. This review aims to present a comprehensive overview of high-velocity microparticle impact techniques to provide a reference for researchers in different materials testing fields and facilitate experimental design in dynamic testing for a wide range of impactor sizes, geometries, and velocities. Next, we review recent studies using the laser-induced particle impact test platform comprising target, projectile, and synergistic target-particle impact response, hence demonstrating the versatility of the method with applications in impact protection and additive manufacturing. We conclude by presenting the future perspectives in the field of high-velocity impact.

We describe a high-speed single-shot multi-frame interferometric imaging technique enabling multiple interferometric images with femtosecond exposure time over a 50 ns event window to be recorded following a single laser-induced excitation event. The stroboscopic illumination of a framing camera is made possible through the use of a doubling cavity which produces a femtosecond pulse train that is synchronized to the gated exposure windows of the individual frames of the camera. The imaging system utilizes a Michelson interferometer to extract phase and ultimately displacement information. We demonstrate the method by monitoring laser-induced deformation and the propagation of high-amplitude acoustic waves in a silicon nitride membrane. The method is applicable to a wide range of fast irreversible phenomena such as crack branching, shock-induced material damage, cavitation and dielectric breakdown.

This paper presents a novel approach to launch single microparticles at high velocities under low vacuum conditions. In an all-optical table-top method, microparticles with sizes ranging from a few microns to tens of microns are accelerated to supersonic velocities depending on the particle mass. The acceleration is performed through a laser ablation process and the particles are monitored in free space using an ultra-high-speed multi-frame camera with nanosecond time resolution. Under low vacuum, we evaluate the current platform performance by measuring particle velocities for a range of particle types and sizes, and demonstrate blast wave suppression and drag reduction under vacuum. Showing an impact on polyethylene, we demonstrate the capability of the experimental setup to study materials behavior under high-velocity impact. The present method is relevant to space applications, particularly to rendezvous missions where velocities range from tens of m/s to a few km/s, as well as to a wide range of terrestrial applications including impact bonding and impact-induced erosion., Comment: 13 pages, 9 figures, keywords: high-velocity launcher; microparticle impact; high-speed imaging; low vacuum; laser-based method; table-top system; ejecta; drag; blast; ballistic limit

In this study a single laser pulse spatially shaped into a ring is focused into a thin water layer, creating an annular cavitation bubble and cylindrical shock waves: an outer shock that diverges away from the excitation laser ring and an inner shock that focuses towards the center. A few nanoseconds after the converging shock reaches the focus and diverges away from the center, a single bubble nucleates at the center. The inner diverging shock then reaches the surface of the annular laser-induced bubble and reflects at the boundary, initiating nucleation of a tertiary bubble cloud. In the present experiments, we have performed time-resolved imaging of shock propagation and bubble wall motion. Our experimental observations of single-bubble cavitation and collapse and appearance of ring-shaped bubble clouds are consistent with our numerical simulations that solve a one dimensional Euler equation in cylindrical coordinates. The numerical results agree qualitatively with the experimental observations of the appearance and growth of bubble clouds at the smallest laser excitation rings. Our technique of shock-driven bubble cavitation opens novel perspectives for the investigation of shock-induced single-bubble or multi-bubble cavitation phenomena in thin liquids.

Understanding material behavior under high velocity impact is the key to addressing a variety of fundamental questions in areas ranging from asteroid strikes and geological cratering to impact-induced phase transformations, spallation, wear, and ballistic penetration. Recently, adhesion has emerged in this spectrum since it has been found that micrometer-sized metallic particles can bond to metallic substrates under supersonic-impact conditions. However, the mechanistic aspects of impact-induced adhesion are still unresolved. Here we study supersonic impact of individual metallic microparticles on substrates with micro-scale and nanosecond-level resolution. This permits the first direct observation of a material-dependent threshold velocity, above which the particle undergoes impact-induced material ejection and adheres to the substrate. Our finite element simulations reveal that prevailing theories of impact-induced shear localization and melting cannot account for the material ejection. Rather, it originates from the propagation of a pressure wave induced upon impact. The experiments and simulations together establish that the critical adhesion velocity for supersonic microparticles is proportional to the bulk speed of sound.

Cylindrically or spherically focusing shock waves have been of keen interest for the past several decades. In addition to fundamental study of materials under extreme conditions, cavitation, and sonoluminescence, focusing shock waves enable myriad applications including hypervelocity launchers, synthesis of new materials, production of high-temperature and high-density plasma fields, and a variety of medical therapies. Applications in controlled thermonuclear fusion and in the study of the conditions reached in laser fusion are also of current interest. Here we report on a method for direct real-time visualization and measurement of laser-driven shock generation, propagation, and 2D focusing in a sample. The 2D focusing of the shock front is the consequence of spatial shaping of the laser shock generation pulse into a ring pattern. A substantial increase of the pressure at the convergence of the acoustic shock front is observed experimentally and simulated numerically. Single-shot acquisitions using a streak camera reveal that at the convergence of the shock wave in liquid water the supersonic speed reaches Mach 6, corresponding to the multiple gigapascal pressure range 30 GPa.